ALBERT

Beschreibung: ▪ Abstract  Sensory responses to the taste, smell, and texture of foods help determine food preferences and eating habits. However, sensory responses alone do not predict food consumption. The view that a “sweet tooth” leads to obesity through excess sugar consumption is overly narrow. In reality, there are multiple links between taste perceptions, taste preferences, food preferences, and food choices and the amount of food consumed. Taste responses are influenced by a range of genetic, physiological, and metabolic variables. The impact of taste factors on food intake further depends on sex and age and is modulated by obesity, eating disorders, and other pathologies of eating behavior. Food preferences and food choices of populations are further linked to attitudinal, social, and—probably most important—economic variables such as income. Nutrition education and intervention strategies aimed at improving population diets ought to consider sensory pleasure response to foods, in addition to a wide range of demographic and sociocultural variables.

Beschreibung: ▪ Abstract  Broadly defined, phytoestrogens include isoflavones, coumestans, and lignans. A number of these compounds have been identified in fruits, vegetables, and whole grains commonly consumed by humans. Soybeans, clover and alfalfa sprouts, and oilseeds (such as flaxseed) are the most significant dietary sources of isoflavones, coumestans, and lignans, respectively. Studies in humans, animals, and cell culture systems suggest that dietary phytoestrogens play an important role in prevention of menopausal symptoms, osteoporosis, cancer, and heart disease. Proposed mechanisms include estrogenic and antiestrogenic effects, induction of cancer cell differentiation, inhibition of tyrosine kinase and DNA topoisomerase activities, suppression of angiogenesis, and antioxidant effects. Although there currently are no dietary recommendations for individual phytoestrogens, there may be great benefit in increased consumption of plant foods.

Beschreibung: Thirty years ago, it was suggested that maternal intake of certain vitamins during pregnancy affected the incidence of serious fetal malformations. Subsequent research has revealed that folate (folic acid), a B vitamin, plays a crucial role in the development of the central nervous system during the early weeks of gestation, which is generally before the pregnancy is confirmed. In a significant number of embryos, an inadequate supply of folate at this time leads to a failure of the primitive neural tube to close and differentiate normally and results in neural tube birth defects (NTD). Numerous studies have confirmed the importance of an adequate intake of folate during the weeks just before and after conception. Overall, the data predict that if women consume multivitamin supplements containing folic acid during the periconceptional period, the number of children born with serious malformations (such as spina bifida and anencephaly) could be reduced by half. Although programs to increase dietary folate intake of potential mothers may be effective in reducing NTD, the only proven and practical preventive measure currently available is to take oral multivitamin supplements containing folic acid. Multivitamin supplementation has also been associated with reduced incidence of other congenital malformations. Current research is focusing on the role of micronutrients in embryogenesis, and on methods to identify prospective mothers at increased risk for bearing a child with NTD or with other major malformations shown to occur at reduced frequency with multivitamin supplementation. Of equal importance is the development of methods to communicate current knowledge as a public health measure.

Beschreibung: Free radicals and antioxidants are widely discussed in the clinical and nutritional literature. Antioxidants are needed to prevent the formation and oppose the actions of reactive oxygen and nitrogen species, which are generated in vivo and cause damage to DNA, lipids, proteins, and other biomolecules. Endogenous antioxidant defenses (superoxide dismutases, H2O2-removing enzymes, metal binding proteins) are inadequate to prevent damage completely, so dietderived antioxidants are important in maintaining health. Many dietary compounds have been suggested to be important antioxidants: The evidence for a key role of vitamins E and C is strong, but that for carotenoids and related plant pigments is weaker. Interest is also growing in the role of plant phenolics, especially flavonoids. Some antioxidants can exert prooxidant effects in vitro, but their physiological relevance is uncertain. Experimental approaches to the optimization of antioxidant nutrient intake are proposed.

Beschreibung: ▪ Abstract  Intracellular lipid-binding proteins are a family of low-molecular-weight single-chain polypeptides that form 1:1 complexes with fatty acids, retinoids, or other hydrophobic ligands. These proteins are products of a large multigene family of unlinked loci distributed throughout the genome. Each lipid-binding protein exhibits a distinctive pattern of tissue distribution. Transcriptional control, regulated by a combination of peroxisome proliferator activated receptors and CCAAT/enhancer-binding proteins, allows for a variety of both cell and tissue-specific expression patterns. In some cells, fatty acids increase the expression of the lipid-binding protein genes. Fatty acids, or their metabolites, are activators of the peroxisome proliferator–activated receptor family of transcription factors. Therefore, as the concentration of lipid in the diet increases, the expression of lipid-binding proteins coordinately increases. As revealed by X-ray crystallography, the lipid-binding proteins fold into β-barrels, forming a large internal water-filled cavity. Fatty acid ligands are bound within the cavity, occupying only about one-third of the accessible volume. The bound fatty acid is stabilized via a combination of enthalpic and entropic forces that govern ligand affinity and selectivity. Cytoplasmic lipid-binding proteins are the intracellular receptors for hydrophobic ligands, delivering them to the appropriate site for use as metabolic fuels and regulatory agents.

Beschreibung: ▪ Abstract  Many microorganisms previously unrecognized as food-borne or harmful are emerging as human pathogens transmitted by food. This is a result of recent acquisition of key virulence factors, detection by newly developed isolation procedures, or astute detective-like laboratory skills of microbiologists. Six microbial pathogens, including Shiga toxin-producing Escherichia coli, Listeria monocytogenes, Arcobacter butzleri, Helicobacter pylori, Cryptosporidium parvum, and Cyclospora, have become recognized as significant causes of human illness. Although the ecology and epidemiology of illness caused by some of these pathogens have not been fully elucidated, food has the potential of being an important vehicle in their dissemination. Existing technologies and new approaches such as irradiation and hazard analysis critical control point (HACCP) programs are useful tools in the control of food-borne hazards. However, because of ever-changing products, processes, food-handling practices, societal habits, and pathogens, emerging food-borne diseases will continue to be an important public health concern.

Beschreibung: ▪ Abstract  Some coffee brewing techniques raise the serum concentration of total and low-density-lipoprotein cholesterol in humans, whereas others do not. The responsible factors are the diterpene lipids cafestol and kahweol, which make up about 1% (wt:wt) of coffee beans. Diterpenes are extracted by hot water but are retained by a paper filter. This explains why filtered coffee does not affect cholesterol, whereas Scandinavian “boiled,” cafetiere, and Turkish coffees do. We describe the identification of the cholesterol-raising factors, their effects on blood levels of lipids and liver function enzymes, and their impact on public health, based on papers published up to December 1996.

Beschreibung: ▪ Abstract  Dietary fat is an important macronutrient for the growth and development of all organisms. In addition to its role as an energy source and its effects on membrane lipid composition, dietary fat has profound effects on gene expression, leading to changes in metabolism, growth, and cell differentiation. The effects of dietary fat on gene expression reflect an adaptive response to changes in the quantity and type of fat ingested. Specific fatty acid–regulated transcription factors have been identified in bacteria, amphibians, and mammals. In mammals, these factors include peroxisome proliferator–activated receptors (PPARα, -β, and -γ), HNF4α, NFκB, and SREBP1c. These factors are regulated by (a) direct binding of fatty acids, fatty acyl–coenzyme A, or oxidized fatty acids; (b) oxidized fatty acid (eicosanoid) regulation of G-protein–linked cell surface receptors and activation of signaling cascades targeting the nucleus; or (c) oxidized fatty acid regulation of intracellular calcium levels, which affect cell signaling cascades targeting the nucleus. At the cellular level, the physiological response to fatty acids will depend on (a) the quantity, chemistry, and duration of the fat ingested; (b) cell-specific fatty acid metabolism (oxidative pathways, kinetics, and competing reactions); (c) cellular abundance of specific nuclear and membrane receptors; and (d) involvement of specific transcription factors in gene expression. These mechanisms are involved in the control of carbohydrate and lipid metabolism, cell differentiation and growth, and cytokine, adhesion molecule, and eicosanoid production. The effects of fatty acids on the genome provide new insight into how dietary fat might play a role in health and disease.

Beschreibung: ▪ Abstract  The field of human body composition research is reaching a mature stage in its development: The three interconnected areas that define body composition research—models and their rules, methodology, and biological effects—are well-defined and are actively investigated by scientists in diverse disciplines from many different nations; and methods are available for measuring all major atomic, molecular, cellular, and tissue-system level body composition components in research, clinical, and epidemiological settings. This review summarizes main body composition research concepts, examines new component-measurement methodologies, and identifies potential areas of future research.

Beschreibung: ▪ Abstract  Factors that influence the bioavailability of carotenoids and their bioconversion to retinol are species of carotenoids, molecular linkage, amount of carotenoids consumed in a meal, matrix in which the carotenoid is incorporated, effectors of absorption and bioconversion, nutrient status of the host, genetic factors, host-related factors, and mathematical interactions. In this paper, current knowledge of these factors is examined. Although data are not sufficiently comparable to allow an extensive systematic comparison of results, a number of conclusions can be drawn from the information available.

Beschreibung: ▪ Abstract  We summarize the recent information on field metabolic rates (FMR) of wild terrestrial vertebrates as determined by the doubly labeled water technique. Allometric (scaling) relationships are calculated for mammals (79 species), reptiles (55 species), and birds (95 species) and for various taxonomic, dietary, and habitat groups within these categories. Exponential equations based on body mass are offered for predicting rates of daily energy expenditure and daily food requirements of free-ranging mammals, reptiles, and birds. Significant scaling differences between various taxa, dietary, and habitat groups (detected by analysis of covariance with P ≤ 0.05) include the following: (a) The allometric slope for reptiles (0.889) is greater than that for mammals (0.734), which is greater than that for birds (0.681); (b) the slope for eutherian mammals (0.772) is greater than that for marsupial mammals (0.590); (c) among families of birds, slopes do not differ but elevations (intercepts) do, with passerine and procellariid birds having relatively high FMRs and gallinaceous birds having low FMRs; (d) Scleroglossan lizards have a higher slope (0.949) than do Iguanian lizards (0.793); (e) desert mammals have a higher slope (0.785) than do nondesert mammals; (f) marine birds have relatively high FMRs and desert birds have low FMRs; and (g) carnivorous mammals have a relatively high slope and carnivorous, insectivorous, and nectarivorous birds have relatively higher FMRs than do omnivores and granivores. The difference detected between passerine and nonpasserine birds reported in earlier reviews is not evident in the larger data set analyzed here. When the results are adjusted for phylogenetic effects using independent contrasts analysis, the difference between allometric slopes for marsupials and eutherians is no longer significant and the slope difference between Scleroglossan and Iguanian lizards disappears as well, but other taxonomic differences remain significant. Possible causes of the unexplained variations in FMR that could improve our currently inaccurate FMR prediction capabilities should be evaluated, including many important groups of terrestrial vertebrates that remain under- or unstudied and such factors as reproductive, thermoregulatory, social, and predator-avoidance behavior.

Beschreibung: ▪ Abstract  Transition metals such as iron, copper, manganese, and zinc are essential nutrients. The yeast Saccharomyces cerevisiae is an ideal organism for deciphering the mechanism and regulation of metal ion transport. Recent studies of yeast have shown that accumulation of any single metal ion is mediated by two or more substrate-specific transport systems. High-affinity systems are active in metal-limited cells, whereas low-affinity systems play the predominant roles when the substrate is more abundant. Metal ion uptake systems of cells are tightly controlled, and both transcriptional and posttranscriptional regulatory mechanisms have been identified. Most importantly, studies of S. cerevisiae have identified a large number of genes that function in metal ion transport and have illuminated the existence and importance of gene families that play related roles in these processes in mammals.

Beschreibung: ▪ Abstract  A growth-promoting principle of the pituitary gland was discovered in 1921, and bovine growth hormone (GH) was isolated in 1944. Since then, the structure of GH as it relates to its biological activities has been an exciting research topic. Equally fascinating is the relationship between GH structure and its metabolic activities. In attempts to define some of these activities, several investigators have used GH transgenic mice as models. In this review we summarize what is known about the molecular mechanisms of GH action. We then describe some of the GH transgenic models and point out potential targets for nutrition research.

Beschreibung: ▪ Abstract  Insulin vasodilates skeletal muscle vasculature via an endothelium-derived nitric oxide–dependent mechanism. Data suggests that insulin interacts directly with the endothelium to cause nitric oxide release. This insulin-mediated increase in muscle perfusion accounts for ∼30% of insulin's overall action to stimulate muscle glucose uptake, suggesting a role for insulin and glucose delivery as a determinant of insulin action. Hindlimb perfusion experiments, where perfusion rate is fixed, suggest that changes in distribution of microcirculatory perfusion can modulate substrate uptake. The potential role of insulin to enhance flow through capillary networks that are efficient at nutrient transfer to tissue (nutritive flow) relative to non-nutritive flow is discussed.

Beschreibung: ▪ Abstract  In vitro studies of adipocytes taken from different body fat regions suggest substantial differences in lipolysis between intra-abdominal, lower-body subcutaneous, and abdominal subcutaneous regions. Gender and obesity appear to influence these regional differences. In situ measurements of glycerol release from adipose tissue provided further evidence that regional heterogeneity of lipolysis occurs in humans. In vivo studies of regional free fatty acid (FFA) release have confirmed that adipose tissue lipolysis varies between upper- and lower-body fat. Release of FFA from lower-body adipose tissue is less than that from upper-body adipose tissue in both obese and non-obese men and women. In non-obese men and women, meal ingestion suppresses FFA release from all adipose tissue regions, and adrenergic stimulation activated FFA release from different sites in a gender-specific fashion. Significant regional and gender differences in adipose tissue lipolysis occur in humans, and this could contribute to differences in the health effects of adipose tissue and could theoretically influence body fat distribution.

Beschreibung: ▪ Abstract  If the function of vitamin E is that of an antioxidant and the various forms of vitamin E have similar antioxidant activities, then why does RRR-α-tocopherol have the highest biologic activity? This chapter describes how interactions by investigators from various scientific disciplines using stable isotopes, molecular biology tools, and sophisticated genetic studies of humans with vitamin E deficiency have led to an understanding of this problem. This chapter provides an overview of (a) studies using deuterated tocopherols that demonstrated that the plasma preference for α-tocopherol is dependent on metabolic processes in the liver; (b) the isolation, molecular biology, and function of the α-tocopherol transfer protein; and (c) studies that demonstrated that patients who were vitamin E deficient as a result of no known cause had defective α-tocopherol transfer protein genes. Finally, we focus on the future—what remains to be learned about the regulation of vitamin E in tissues.

Beschreibung: During vigorous exercise, carbohydrate, in the form of muscle glycogen and blood glucose, is the primary energy source, whereas fatty acids play a secondary, carbohydrate-sparing role. In the postabsorptive state, nearly all of the carbohydrate used during exercise comes from muscle and liver glycogen. The size of these glycogen stores plays a major role in determining how long vigorous endurance exercise can be performed if other causes of fatigue, such as dehydration or heat exhaustion, are avoided. In a “fight or flight” situation, individuals whose muscles are glycogen depleted are helpless, as they are unable to either run or fight. The same is true of someone who has become markedly hypoglycemic as a result of liver glycogen depletion.

Beschreibung: ▪ Abstract  Cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) are members of the lipid transfer/lipopolysaccharide binding protein gene family. Recently, the crystal structure of one of the members of the gene family, bactericidal permeability increasing protein, was solved, providing potential insights into the mechanisms of action of CETP and PLTP. These molecules contain intrinsic lipid binding sites and appear to act as carrier proteins that shuttle between lipoproteins to redistribute lipids. The phenotype of human CETP genetic deficiency states and CETP transgenic mice indicates that CETP plays a major role in the catabolism of high-density lipoprotein (HDL) cholesteryl esters and thereby influences the concentration, apolipoprotein content, and size of HDL particles in plasma. PLTP also appears to have an important role in determining HDL levels and speciation. Recent data indicate that genetic CETP deficiency is associated with an excess of coronary heart disease in humans, despite increased HDL levels. Also, CETP expression is anti-atherogenic in many mouse models, even while lowering HDL. These data tend to support the reverse cholesterol transport hypothesis, i.e. that anti-atherogenic properties of HDL are related to its role in reverse cholesterol transport. Recently, another key molecule involved in this pathway was identified, scavenger receptor BI; this mediates the selective uptake of HDL cholesteryl esters in the liver and thus constitutes a pathway of reverse cholesterol transport parallel to that mediated by CETP. Reflecting its role in reverse cholesterol transport, the CETP gene is up-regulated in peripheral tissues and liver in response to dietary or endogenous hypercholesterolemia. An analysis of the CETP proximal promoter indicates that it contains sterol regulatory elements highly homologous to those present in 3-hydroxy-3-methylglutaryl-coenzyme A reductase; the CETP gene is transactivated by the binding of SREBP-1 to these elements. A challenge for the future will be the manipulation of components of the reverse cholesterol transport pathway, such as CETP, PLTP, or scavenger receptor BI for therapeutic benefit.

Beschreibung: We first present a brief discussion of early and current models (feeding systems) used to estimate animal energy and protein requirements and to predict performance based on feed composition and intake. We then touch on some limitations inherent in these systems. Next, we propose that dynamic (i.e. time-variant) models and mechanistic models (i.e. equations based on knowledge of physiological functions) are superior to earlier systems for both practical and research applications. Finally, we describe a number of applied and research models of animal growth and lactation to illustrate how biological concepts may be represented in equation form. Equations that represent current knowledge of underlying functions can be used to improve predictions of animal requirements and performance and to evaluate hypotheses about nutritional and physiological mechanisms that influence animal performance.

Beschreibung: ▪ Abstract  Carnitine functions as a substrate for a family of enzymes, carnitine acyltransferases, involved in acyl-coenzyme A metabolism and as a carrier for long-chain fatty acids into mitochondria. Carnitine biosynthesis and/or dietary carnitine fulfill the body's requirement for carnitine. To date, a genetic disorder of carnitine biosynthesis has not been described. A genetic defect in the high-affinity plasma membrane carnitine-carrierin leads to renal carnitine wasting and primary carnitine deficiency. Myopathic carnitine deficiency could be due to an increase in efflux moderated by the carnitine-carrierout. Defects in the carnitine transport system for fatty acids in mitochondria have been described and are being examined at the molecular and pathophysiological levels. The nutritional management of these disorders includes a high-carbohydrate, low-fat diet and avoidance of those events that promote fatty acid oxidation, such as fasting, prolonged exercise, and cold. Large-dose carnitine treatment is effective in systemic carnitine deficiency.

Beschreibung: [Figure: see text] ▪ Abstract  As Jackie Gleason was wont to say: “How sweet it really is!” And—reflecting on the 1940s–1980s, when studies of microbial nutrition revealed exciting structure-function relationships of the B-complex vitamins with relevance to metabolism in humans—it really is. A chemistry degree from Beloit College and a doctorate in biochemistry from the University of Wisconsin set the stage for my life's work at Lederle Laboratories, the University of Illinois, and Vanderbilt University. At Lederle my research contributed to folic acid chemistry: coenzyme forms and function; antimetabolites and cancer chemotherapy. My subsequent university studies centered on lysine biosynthesis and metabolism, e.g. its precursor role in carnitine and in indolizidine alkaloids of physiological interest. There were also many opportunities to reach out and give something back to the system via teaching and diverse service activities, all of which has led to a happy, fulfilling career, one for which I am ever thankful.

Beschreibung: ▪ Abstract  Psychosocial variables that predict dietary behavior become important targets for change in nutrition education programs. Psychosocial variables in models with higher predictability provide more effective levers to promote healthy dietary change. A review of the literature on models with psychosocial variables predicting dietary fat and fruit and vegetable consumption revealed generally low predictiveness, R2 〈 0.3 (where R2 is the squared multiple correlation of the statistical model). No single theory provided models that regularly out-predicted others. When models predicted narrower categories of behavior (e.g. milk or salad consumption), predictiveness tended to be higher. Substantial problems were revealed in the psychometrics of both the independent and dependent variables. Little theory-based research has been conducted with adolescents, and the few studies done with children had low predictiveness. In order to increase the predictiveness of models, future research should combine variables from several theories, attend to the psychometrics of all variables, and incorporate variables that moderate the relationship of psychosocial to dietary behavior (e.g. genetics of taste, stage in the life course). Refinements on current research would include longitudinal designs and use of non–self-report methods of dietary behavior to supplement the self-report methods. Improved understanding of dietary behavior should lead to more effective dietary behavior change interventions.

Beschreibung: ▪ Abstract  Polyketides constitute a huge family of structurally diverse natural products including antibiotics, chemotherapeutic compounds, and antiparasitics. Most of the research on polyketide synthesis in bacteria has focused on compounds synthesized by Streptomyces or other actinomycetes; however, plant-associated pseudomonads also produce a variety of compounds via the polyketide pathway including the phytotoxin coronatine, the antibiotic mupirocin, and the antifungal compounds pyoluteorin and 2,4-diacetylphloroglucinol. This review focuses on the mode of action, regulation, biosynthesis, and genetics of these four compounds and the potential use of Pseudomonas-derived polyketide synthases in the generation of novel compounds with unique activities.

Beschreibung: ▪ Abstract  Microbial population dynamics on leaves in time and space are a function of immigration, emigration, growth, and death. Insight into the relative significance of each population process to the generation of specific dynamics for individual microorganisms is necessary to understanding the ecology and life history strategy of the microorganism and to developing effective control strategies. Additionally, information on the significance of within-leaf versus extra-leaf processes to the generation of phyllosphere dynamics is important to determining the range of spatial scales over which a population should be studied. Unfortunately, such information is difficult to obtain due to the lack of effective methodologies for distinguishing these processes within phyllosphere populations. Future research efforts should focus on the quantification of immigration, emigration, growth, and death relative to the population dynamics of phyllosphere microorganisms.

Beschreibung: ▪ Abstract  In ascomycetes, the single mating type locus (MAT) controls sexual development. This locus is structurally unusual because the two alternate forms (“alleles”) are completely dissimilar sequences, encoding different transcription factors, yet they occupy the same chromosomal position. Recently developed procedures allow efficient cloning of MAT genes from a wide array of filamentous ascomycetes, thereby providing MAT-based technology for application to several ongoing issues in fungal biology. This article first outlines the basic nature of MAT genes, then addresses the following topics: efficient cloning of MAT genes; the unusual molecular characteristics of these genes; phylogenetics using MAT; the issues of why some fungi are self-sterile, others self-fertile, and yet others asexual; the long-standing mystery of possible mating type switching in filamentous fungi; and finally the evolutionary origins of pathogenic capability.

Beschreibung: ▪ Abstract  Quantitative trait locus (QTL) mapping is a highly effective approach for studying genetically complex forms of plant disease resistance. With QTL mapping, the roles of specific resistance loci can be described, race-specificity of partial resistance genes can be assessed, and interactions between resistance genes, plant development, and the environment can be analyzed. Outstanding examples include: quantitative resistance to the rice blast fungus, late blight of potato, gray leaf spot of maize, bacterial wilt of tomato, and the soybean cyst nematode. These studies provide insights into the number of quantitative resistance loci involved in complex disease resistance, epistatic and environmental interactions, race-specificity of partial resistance loci, interactions between pathogen biology, plant development and biochemistry, and the relationship between qualitative and quantitative loci. QTL mapping also provides a framework for marker-assisted selection of complex disease resistance characters and the positional cloning of partial resistance genes.

Beschreibung: ▪ Abstract  Epichloë species and their asexual descendants (Acremonium endophytes) are fungal symbionts of C3 grasses that span the symbiotic continuum from antagonism to mutualism depending on the relative importance, respectively, of horizontal transmission of sexual spores versus vertical clonal transmission in healthy grass seeds. At least seven sexual Epichloë species are identifiable by mating tests, and many asexual genotypes are interspecific hybrids. Benefits conferred by the symbionts on host plants include protection from biotic factors and abiotic stresses such as drought. Four classes of beneficial alkaloids are associated with the symbionts: ergot alkaloids, indolediterpenes (lolitrems), peramine, and saturated aminopyrrolizidines (lolines). These alkaloids protect host plants from insect and vertebrate herbivores, including livestock. Genetic engineering of the fungal symbionts as more suitable biological protectants for forage grasses requires identification of fungal genes for alkaloid biosynthesis, and DNA-mediated transformation of the fungi.

Beschreibung: ▪ Abstract  This paper examines induced resistance (SAR) in plants against various insect and pathogenic invaders. SAR confers quantitative protection against a broad spectrum of microorganisms in a manner comparable to immunization in mammals, although the underlying mechanisms differ. Discussed here are the molecular events underlying SAR: the mechanisms involved in SAR, including lignification and other structural barriers, pathogenesis-related proteins and their expression, and the signals for SAR including salicylic acid. Recent findings on the biological role of systemin, ethylene, jasmonates, and electrical signals are reviewed. Chemical activators of SAR comprise inorganic compounds, natural compounds, and synthetic compounds. Plants known to exhibit SAR and induced systemic resistance are listed.

Beschreibung: ▪ Abstract  Thirty soilborne viruses or virus-like agents are transmitted by five species of fungal vectors. Ten polyhedral viruses, of which nine are in the family Tombusviridae, are acquired in the in vitro manner and do not occur within the resting spores of their vectors, Olpidium brassicae and O. bornovanus. Fungal vectors for other viruses in the family should be sought even though tombusviruses are reputed to be soil transmitted without a vector. Eighteen rod-shaped viruses belonging to the furo- and bymovirus groups and to an unclassified group are acquired in the in vivo manner and survive within the resting spores of their vector, O. brassicae, Polymyxa graminis, P. betae, and Spongospora subterranea. The viral coat protein has an essential role in in vitro transmission. With in vivo transmission a site in the coat protein-read through protein (CP-RT) of beet necrotic yellow vein furovirus determines vector transmissibility as does a site in a similar 98-kDa polyprotein of barley mild mosaic bymovirus. The mechanisms by which virions move (or are moved) into and out of the protoplasm of zoospores or of thalli needs study.

Beschreibung: Capsid proteins of a number of plant viruses are permissive to genetic modifications in which foreign polypeptides are inserted in exposed loops or at their C termini. Plant viruses with these genetic alterations often grow at wild-type levels, providing gram quantities of modified viruses. Presented polypeptides studied most extensively correspond to antigenic epitopes of animal viruses and in some cases appropriately altered plant viruses generate neutralizing antibodies to the cognate animal virus when the plant virus is used as a vaccine. Structure-based analyses of these animal-plant virus chimeras have led to rational alterations to the presentation in efforts to increase the efficacy of the presented peptide.

Beschreibung: ▪ Abstract  Nonpathogenic rhizobacteria can induce a systemic resistance in plants that is phenotypically similar to pathogen-induced systemic acquired resistance (SAR). Rhizobacteria-mediated induced systemic resistance (ISR) has been demonstrated against fungi, bacteria, and viruses in Arabidopsis, bean, carnation, cucumber, radish, tobacco, and tomato under conditions in which the inducing bacteria and the challenging pathogen remained spatially separated. Bacterial strains differ in their ability to induce resistance in different plant species, and plants show variation in the expression of ISR upon induction by specific bacterial strains. Bacterial determinants of ISR include lipopolysaccharides, siderophores, and salicylic acid (SA). Whereas some of the rhizobacteria induce resistance through the SA-dependent SAR pathway, others do not and require jasmonic acid and ethylene perception by the plant for ISR to develop. No consistent host plant alterations are associated with the induced state, but upon challenge inoculation, resistance responses are accelerated and enhanced. ISR is effective under field conditions and offers a natural mechanism for biological control of plant disease.

Beschreibung: ▪ Abstract  Plant viruses utilize several mechanisms to generate the large amount of genetic diversity found both within and between species. Plant RNA viruses and pararetroviruses probably have highly error prone replication mechanisms, that result in numerous mutations and a quasispecies nature. The plant DNA viruses also exhibit diversity, but the source of this is less clear. Plant viruses frequently use recombination and reassortment as driving forces in evolution, and, occasionally, other mechanisms such as gene duplication and overprinting. The amount of variation found in different species of plant viruses is remarkably different, even though there is no evidence that the mutation rate varies. The origin of plant viruses is uncertain, but several possible theories are proposed. The relationships between some plant and animal viruses suggests a common origin, possibly an insect virus. The propensity for rapid adaptation makes tracing the evolutionary history of viruses difficult, and long term control of virus disease nearly impossible, but it provides an excellent model system for studying general mechansims of molecular evolution.

Beschreibung: ▪ Abstract  The 15 known viruses that occur in rice are rice black-streaked dwarf, rice bunchy stunt, rice dwarf, rice gall dwarf, rice giallume, rice grassy stunt, rice hoja blanca, rice necrosis mosaic, rice ragged stunt, rice stripe necrosis, rice stripe, rice transitory yellowing, rice tungro bacilliform, rice tungro spherical, and rice yellow mottle viruses. This paper describes their geographical distribution, relation to vectors, infection cycles, field dispersal, and development, and lists recorded outbreaks of the viruses. Many rice viruses have become serious problems since rice cultivation has been intensified. Double-cropping of rice using improved, photo-insensitive cultivars of short growth duration has significantly influenced the incidence of these viruses.

Beschreibung: ▪ Abstract  Genetic analyses of the rp1 rust resistance complex of maize have demonstrated that recombination plays a central role in the creation of genetic diversity at the locus. The generation of rp1 diversity is promoted by a high rate of intragenic recombination coupled with a tendency for genes in the complex to mispair in meiosis. Among the novel rp1 genes that have been identified include genes with novel race-specificities and genes conferring lesion mimic phenotypes. Recombinants have also been identified that confer partial resistance which is apparently non-race-specific and may be useful in controlling maize rusts in a durable manner.

Beschreibung: ▪ Abstract  Infection structures of phytopathogenic fungi are modified hyphae specialized for the invasion of plant tissues. Initial events are adhesion to the cuticle and directed growth of the germ tube on the plant surface. At the site of penetration, appressoria are often formed that may have melanized walls and develop high turgor pressure to support the penetration process. The penetration hypha accumulates components of the cytoskeleton in the tip and secretes a variety of cell wall–degrading enzymes in a highly regulated fashion in order to penetrate the cuticle and the plant cell wall. This article reviews recent papers on the cytology, physiology, and molecular biology of the penetration process.

Beschreibung: This review focuses on the role of two distinct fitness strategies in the growth, survival, and epidemiology of foliar bacterial pathogens. A tolerance strategy requires the ability to tolerate direct exposure to environmental stresses on leaf surfaces, including UV radiation and low water availability. An avoidance strategy requires the ability to seek and/or exploit sites that are protected from these stresses, including endophytic sites. The ability to employ an avoidance strategy and grow endophytically may directly influence the potential for pathogenesis, since endophytic populations, not epiphytic populations, are likely responsible for disease induction. Furthermore, exchange between these two populations is probably crucial to the epidemiology of foliar pathogens. While foliar pathogens can grow and survive in both exposed and internal sites, indicating that they can employ both fitness strategies, the poor internal growth of most saprophytes suggests that saprophytes depend primarily on a strategy of tolerance. This difference between pathogens and saprophytes has important implications for predicting the population dynamics of leaf-associated bacterial species and for selecting effective biological control agents.

Beschreibung: ▪ Abstract  One of the best and longest-studied defense response of plants to infection is the induced accumulation of antimicrobial, low-molecular-weight secondary metabolites known as phytoalexins. Since the phytoalexin hypothesis was first proposed in 1940, a role for these compounds in defense has been revealed through several experimental approaches. Support has come, for example, through studies on the rate of phytoalexins in relation to cessation of pathogen development, quantification of phytoalexins at the infection site, and relationship of pathogen virulence to the phytoalexin tolerance. Evidence in support of phytoalexins in resistance as well some recent advances in phytoalexin biosynthesis are reviewed. Criteria for evaluating a role for phytoalexins in disease resistance are also discussed.

Beschreibung: Barley yellow dwarf viruses represent one of the most economically important and ubiquitous groups of plant viruses. This review focuses primarily on four research areas in which progress has been most rapid. These include (a) evidence supporting reclassification of BYDVs into two genera; (b) elucidation of gene function and novel mechanisms controlling gene expression; (c) initial forays into understanding the complex interactions between BYDV virions and their aphid vectors; and (d ) replication of a BYDV satellite RNA. Economic losses, symptomatology, and means of control of BYD are also discussed.

Beschreibung: ▪ Abstract  Farmers increasingly leave crop residues on the soil surface rather than incorporating them into the soil. This practice helps reduce soil erosion, conserve energy, increase soil moisture, and increase crop yields. However, many soilborne plant pathogens survive in the previous year's crop residue, making diseases more problematic under reduced-tillage conditions. Reduced tillage can favor pathogens by such mechanisms as protecting the pathogen's refuge in the residue from microbial degradation, lowering soil temperature, increasing soil moisture, and leaving soil undisturbed. In order for reduced tillage to become more popular, additional controls are needed for pathogens. The four major control tactics (disease-control chemicals, biological control, host resistance, and cultural controls) can be used to limit damage from diseases. It is highly recommended, however, that crop rotation be coupled with reduced tillage. This practice controls many diseases and yet allows as much of the crop residue as possible to be retained on the soil surface.

Beschreibung: ▪ Abstract  The Red Queen Hypothesis (RQH) explains how pathogens may maintain sexual reproduction in hosts. It assumes that parasites become specialized on common host genotypes, reducing their fitness. Such frequency-dependent selection favors sexual reproduction in host populations. Necessary conditions are that resistance and virulence are genotype specific so that host genotype frequencies respond to changes in pathogen genotype frequencies, and vice versa. Empirical evidence on the genetic basis of disease, variation in resistance and virulence, and patterns of infection in sexual and asexual plants support certain features of the hypothesis. However, gene-for-gene interactions are generally not consistent with the RQH because they do not result in cycling of gene frequencies, unlike a matching allele mechanism. A conclusion of whether the RQH can explain the maintenance of sexual reproduction cannot be reached at present. Nevertheless, the RQH theory has shed light on many aspects of plant/pathogen interactions important for reducing pathogen damage in agricultural systems.

Beschreibung: ▪ Abstract  Viruses in the genus Tenuivirus (Tenuiviruses) cause a number of important diseases in economically important crop plants including rice and maize. Tenuiviruses are transmitted from plant to plant by specific planthopper vectors, and their transmission relationship is circulative-propagative. Thus, Tenuiviruses have host ranges including plants and animals (planthoppers). Four or five characteristic, circular ribonucleoprotein particles (RNPs), each containing a single Tenuivirus genomic RNA, can be isolated from Tenuivirus-infected plants. The genomic RNAs range in size from ca 9.0 kb to 1.3 kb and together give a total genome size of ca 18–19 kb. The genomic RNAs are either negative-sense or ambisense, and expression of the ambisense RNAs utilizes cap-snatching during mRNA transcription. The combination of characteristics exhibited by Tenuiviruses are quite different than those found for most plant viruses and are more similar to vertebrate-infecting viruses in the genus Phlebovirus of the Bunyaviridae.

Beschreibung: ▪ Abstract  Phylogenetic and population genetic methods that compare nucleic acid variation are being used to identify species and populations of pathogenic fungi and determine how they reproduce in nature. These studies show that asexual or sexual reproductive morphology does not necessarily correlate with clonal or recombining reproductive behavior, and that fungi with all types of reproductive morphologies and behaviors can be accommodated by a phylogenetic species concept. Although approximately one fifth of described fungi have been thought to be asexual and clonal, recent studies have shown that they are also recombining. Whether a particular pathogen reproduces clonally or by recombination depends on factors relating to its biology and its distribution in space and time. Knowing the identity of species and populations and their reproductive modes, while taking a broad view of pathogen behavior in space and time, should enhance the ability of pathologists to control pathogens and even predict their behavior.

Beschreibung: ▪ Abstract  hrp genes control the ability of phytopathogenic bacteria to cause disease and to elicit hypersensitive reactions on resistant plants. Genetic and biochemical studies have demonstrated that Hrp proteins are components of Type III secretion systems, regulatory proteins, proteinaceous elicitors of the hypersensitive reaction, and enzymes needed for synthesis of periplasmic glucans. Significantly, Type III secretion systems are involved with the secretion of pathogenicity proteins in bacterial pathogens of animals. The transcriptional activation of a number of bacterial avirulence (avr) genes is controlled by Hrp regulatory proteins, and recent experimental evidence suggests that Avr proteins may be transported by Hrp secretion systems. It has also been hypothesized that pathogenicity and/or virulence gene products exit bacterial phytopathogens via Hrp pathways. Thus, hrp genes may be one of the most important groups of genes found in phytopathogenic bacteria in relationship to pathogenicity and host range.

Beschreibung: ▪ Abstract  Leaf rust (caused by Puccinia recondita f. sp. tritici) is the most widespread and regularly occurring rust on wheat. Genetic resistance is the most economical method of reducing yield losses due to leaf rust. To date, 46 leaf rust resistance genes have been designated and mapped in wheat. Resistance gene expression is dependent on the genetics of host-parasite interaction, temperature conditions, plant developmental stage, and interaction between resistance genes with suppressors or other resistance genes in the wheat genomes. Genes expressed in seedling plants have not provided long-lasting effective leaf rust resistance. Adult-plant resistance genes Lr13 and Lr34 singly and together have provided the most durable resistance to leaf rust in wheat throughout the world. Continued efforts to isolate, characterize, and map leaf rust resistance genes is essential given the ability of the leaf rust fungus to overcome deployed resistance genes.

Beschreibung: ▪ Abstract  Beneficial plant-associated microbes can profoundly influence plant health by suppressing disease, enhancing nutrient uptake, fixing atmospheric nitrogen, and promoting plant growth. Host variation, among cultivars or plant genotypes, for response to beneficial microorganisms suggests that plant genes play a role in supporting these interactions. Such host variation can be found among diverse groups of microorganisms including rhizobia, mycorrhizal fungi, and microbial biocontrol agents. Discrete variation among plant genotypes for interaction with beneficial microbes has led to the discovery of single genes that specify compatible interactions. Continuous variation for interaction phenotypes such as disease suppression, plant growth, or nutrient uptake have led to hypotheses, and in some cases genetic descriptions, of multigenic control of these interactions. Future research into the role of plant genes involved in hosting beneficial plant-associated microbes will provide greater insight into this relatively unexplored area of biology and should provide new tools to improve plant health in agriculture.

Beschreibung: ▪ Abstract  Suppression of the blossom-blight phase of fire blight is a key point in the management of this destructive and increasingly important disease of apple and pear. For blossom infection to occur, the causal bacterium, Erwinia amylovora, needs to increase its population size through an epiphytic phase that occurs on stigmatic surfaces. Knowledge of the ecology of the pathogen on stigmas has been key to the development of predictive models for infection and optimal timing of antibiotic sprays. Other bacterial epiphytes also colonize stigmas where they can interact with and suppress epiphytic growth of the pathogen. A commercially available bacterial antagonist of E. amylovora (BlightBan, Pseudomonas fluorescens A506) can be included in antibiotic spray programs. Integration of bacterial antagonists with chemical methods suppresses populations of the pathogen and concomitantly, fills the ecological niche provided by the stigma with a nonpathogenic, competing microorganism. Further integration of biologically based methods with conventional management of blossom blight may be achievable by increasing the diversity of applied antagonists, by refining predictive models to incorporate antagonist use, and by gaining an improved understanding of the interactions that occur among indigenous and applied bacterial epiphytes, antibiotics, and the physical environment.

Beschreibung: ▪ Abstract  Begomoviruses have circular single-stranded DNA genomes, cause many diseases of dicotyledons in areas with warm climates and are transmitted by whiteflies of the Bemisia tabaci complex. Their genomic and antigenic variation represents geography-related lineages that have little relation to host range. Genomic variation resulting from mutation is amplified by acquisition of extra DNA components, pseudo-recombination and recombination, both intraspecific and interspecific. Recombination, especially interspecific recombination, seems the key mechanism for generating novel virus forms, for enhancing biological fitness of pseudo-recombinants derived from closely related species and for maintaining the flow of genetic material among different geminiviruses occurring in the same geographical region. Recent begomovirus epidemics reflect favorable conjunctions of plant, vector, and viral (e.g. emergence of a novel recombinant virus) factors. Such epidemics typically result in co-infection of plants with different begomoviruses, leading to the appearance of further variants, especially recombinants. In their patterns of variation and evolution, begomoviruses differ greatly from plant viruses with RNA genomes.

Beschreibung: ▪ Abstract  The role and functioning of the anterior chemosensory organs of plant parasitic nematodes is examined, with particular emphasis on the amphids. The morphology of the amphids is discussed primarily in the context of the changes in the ultrastructure associated with different life stages. The involvement of amphidial secretions in chemoreception and the behavioral and electrophysiological analyses of nematode responses to semiochemicals are discussed with special reference to research on sex pheromones. These research techniques, combined with the use of lectins and antibodies, provide information on nematode sensilla that may lead to novel control strategies for economically important plant parasitic nematodes based on perturbing nematode sensory perception to prevent host or mate location.

Beschreibung: ▪ Abstract  Not until 1973 was it reported that strains of Agrobacterium that cause crown gall disease of grape form a specific group (later characterized as Agrobacterium vitis). Tumorigenic and nontumorigenic A. vitis have since been isolated from infected and symptomless grapes worldwide. Research on the genetic makeup of A. vitis has led to an improved understanding of pathogen biology and bacterial evolution. In addition, the identification of significant gene sequences has facilitated the development of PCR and RFLP-based identification procedures that continue to improve the detection of A. vitis in plants and soil. Current control practices rely on the use of disease-resistant cultivars, cultural practices that minimize plant injury, and the production of pathogen-free vines. Promising future controls include employment of biological control agents and development of crown gall–resistant transgenic grapevines.

Beschreibung: ▪ Abstract  Many plant-associated bacteria produce and utilize diffusible N-acyl-homoserine lactones (AHLs) to regulate the expression of specific bacterial genes and operons. AHL-mediated regulation utilizes two genes that encode proteins similar to the LuxI/LuxR system originally studied in the marine symbiont Vibrio fischeri. The LuxI-type proteins are AHL synthases that assemble the diffusible AHL signal. The LuxR-type proteins are AHL-responsive transcriptional regulatory proteins. LuxR proteins control the transcription of specific bacterial genes in response to the levels of AHL signal. To date, AHL-mediated gene regulation has been identified in a broad range of gram-negative bacteria, most of which are host-associated. However, it seems unlikely that such a widely conserved regulatory mechanism would be limited only to host-microbe interactions. These signals probably play central roles in ecological interactions among organisms in microbial communities by affecting communication among bacterial populations as well as between bacterial populations and their eukaryotic hosts.